Communication systems link together communication devices so that the devices can send information to each other in a call or other communication event. Information may include voice, text, images or video.
One such communication system is a peer to peer communication system, in which a plurality of end users can be connected for communication purposes via a communications structure such as the internet using peer to peer client software. The communications structure is substantially decentralised with regard to communication route switching therein for connecting the end users. That is, the end users can establish their own communication routes through the structure based on exchange of one or more authorisation certificates (user identity certificates—UIC) to acquire access to the structure. The structure includes an administration arrangement issuing the certificates to the end users. Such a communication system is described in WO 2005/009019.
Peer-to-peer systems and other communication systems that use the internet or any other packet switched network employ voice over IP (internet protocol) protocols (VoIP) to transmit data. These systems are commonly referred to as VoIP systems. VoIP systems are beneficial to the user as they are often of significantly lower cost than communication networks, such as fixed line or mobile networks, otherwise referred to as public switched telephone networks (PSTN). This may particularly be the case for long distance calls.
In a communication system, such as a peer to peer system, client software is installed on end user devices such as personal computers (PCs) to allow the end users to communicate via the internet. The user interface of the device can be controlled by the client software to display user facilities and to indicate events occurring, such as an incoming call.
Users may be accustomed to mobility whilst using conventional telephony services, due to the prevalence of cordless phones and mobile cellular networks. It is therefore desirable to run the client software on mobile devices such as a mobile phone or other battery operated cordless device. However, running the client software on a mobile end user device presents a number of problems. Hand held mobile devices are typically battery operated and have less CPU resource than a PC. The power requirement used to run the client software to handle the communications can reduce the battery life considerably for battery operated devices. Furthermore, running the client software on the user device may use valuable CPU resources that are required to run other applications on the device.
One further problem caused by using a mobile device in an VoIP communication system is that in a VoIP system such as a peer to peer system, it is necessary to be constantly connected to the internet in order to be notified of communication events, such as receiving a call. Maintaining a constant connection between the communication network and the internet is not only an inefficient use of battery life and CPU resources of the device, but also an inefficient use of network connection resources.